This proposal addresses an important element of the current tuberculosis global epidemic, namely the fact, recently stated in a document released by the NIAID, that we know next to nothing about the newly emerging clinical isolates of M. tuberculosis, many of which are W-Beijing strains. We will test the simple hypothesis here that such strains associated with high rates of transmission are simply more virulent than low transmission strains, with a secondary hypothesis being that the more virulent strains escape acquired immunity by generating regulatory T cells. These simple studies will provide important basic information about the relationship between transmissibility and virulence, and are doable within the context of an R21 application.